The following summary of the main topics of the Program-Project includes studies recently completed, under-way or proposed for the grant year: (1) Polyadenylation of RNA after fertilization (Wilt). Cytoplasmic localization of polyadenylation. Stimulation of polyadenylation in unfertilized eggs with ammonia. Mechanism of polyadenylation and isolation and characterization of enzymes. (2) Histones and nonhistone proteins of chromatin in development (Wilt, Mazia). Histones and nonhistone protein in chromatin of sperm and in male pronuclei after fertilization. Nonhistone proteins in the mitotic cycle and through development. Histones and nonhistone proteins in macromeres and micromere. (3) Electrobiology of fertilization (Mazia in collaboration with R. Steinhardt). Electrode study of membrane changes associated with sperm-egg fusion and with block to polyspermy. Study of changes at fertilization and cell division with intracellular ion-sensitive electrodes. (4) Regulation of chromosome cycle and formation of mitotic apparatus (Mazia). Premature chromosome condensation and formation of mitotic apparatus when chromosome cycle is started in unfertilized eggs some time before fertilization. Chromosome cycles in cells which can not form a mitotic apparatus. (5) Myosin synthesis in cell cultures and in a cell free system (Strohman). Appearance of myosin heavy chains after fusion of myoblasts; synthesis of chains at linearly accelerating rate. Isolation of myosin-mRNA during early differentiation of muscle; evidence that it appears only after fusion. Attempt to obtain myosin-mRNA from whole cell RNA.